2-Butyl-3-[p-(o-1H-tetrazol-5-ylphenyl)benzyl]-1,3-diazaspiro[4.4]non-1-en-4-one, is generically known as Irbesartan. Irbesartan is a non-peptide angiotensin II antagonist, which antagonizes the physiologic effects of angiotensin II by inhibiting the action of angiotensin II on its receptors, the compounds particularly prevent increase in blood pressure produced by the receptor interaction. Irbesartan is approved for the treatment of hypertension and is marketed in the US with the Brand Name, Avapro.
Elf Sanofi, first time disclosed Irbesartan and its pharmaceutically acceptable salts in U.S. Pat. No. 5,270,317.
U.S. Pat. No. 5,399,578 describes two different processes for the preparation of Irbesartan which are subsequently claimed in U.S. Pat. No. 5,559,233. One of the processes involves the reaction of 2-n-butyl-4-spirocyclopentane-2-imidazolin-5-one (II) with 4-bromomethyl-2-cyanobiphenyl (III) in the presence of NaH, followed by a column chromatography separation to yield 1-[(2′-cyanobiphenyl-4-yl)methyl]-2-n-butyl-4-spirocyclopentane-2-imidazolin-5-one (IV). This compound (IV) is further reacted with tributyltin azide and the product treated with trityl chloride and separated by column chromatography. Finally, trityl protected irbesartan (V) is de-protected with hydrochloric acid and the final Irbesartan product is isolated.
The process is as shown in Scheme-I:

The second process described in this patent for the preparation of Irbesartan, is as shown in Scheme-II:

The major disadvantages with the above processes for the preparation of Irbesartan, involve a large number of steps such as protection and deprotection and tedious work-up procedures to isolate the required product. This results in more production time, which in turn renders the process more costly and less eco friendly. Further the above processes are low yielding and yield product of less purity.
WO 2005/113518 A1 describes an alternative process for the preparation of Irbesartan which involves reacting N-pentanoylaminocyclopentanecarboxylic acid (XI) with 2-(4-aminomethylphenyl)benzonitrile (VII) using dicyclohexylcarbodiimide and 1-hydroxybenzotriazole as a catalyst to produce the 4-[(α-N-pentanoylamino)cyclopentamidomethyl]-2-cyanobiphenyl (XII), and then cyclizing using trifluoroacetic acid to result 1-[(2′-cyanobiphenyl-4-yl)methyl]-2-n-butyl-4-spirocyclopentane-2-imidazolin-5-one (IV), which is finally converted to Irbesartan (I) by reaction with tributyl tin chloride and sodium azide.
The process is as shown in Scheme-III below:

We have now developed another process to prepare Irbesartan, which is novel and commercially viable process.